High quality isolation transformers typically are wire wound transformers, which are large and expensive. To shrink the size of such transformers, while keeping high isolation rating is very challenging for smaller footprint designs. There is a big demand for a small, affordable isolation transformer which would be better suited for module integration. Currently, many transformer structure designs can meet these requirements. The planar transformer structure, the planar transformer structure with a center post, as well as EI, UI, and TU-shaped transformers structures, have very high coupling, inductance density and quality factor. However, the transformer core pieces are interconnected by dispensing non-magnetic materials on the laminates for electrical connection. This method will generate “gaps” of 20-25 um thickness between magnetic pieces and laminate winding structures, which has adverse impact on the efficiency and properties of the transformer structures. Better solutions are needed for improved high frequency operation and low-cost manufacturing of planar passive component structures.